Too dog tired to avoid danger: Self-control depletion in canines increases behavioral approach toward
an aggressive threat.
Holly C. Miller & C. Nathan DeWall & Kristina Pattison &
Mikaël Molet & Thomas R. Zentall
# Psychonomic Society, Inc. 2012
This study investigated whether initial selfcontrol
exertion by dogs would affect behavioral approach
toward an aggressive threat. Dogs were initially required to
exert self-control (sit still for 10 min) or not (caged for
10 min) before they were walked into a room in which a
barking, growling dog was caged. Subject dogs spent 4 min
in this room but were free to choose where in the room they
spent their time. Approaching the unfamiliar conspecific
was the predisposed response, but it was also the riskier
choice (Lindsay, 2005). We found that following the exertion
of self-control (in comparison with the control condition),
dogs spent greater time in proximity to the aggressor.
This pattern of behavior suggests that initial self-control
exertion results in riskier and more impulsive decision making
Keywords Self-regulation . Dogs . Decision making . Risk
taking . Impulsivity
The potential for danger is ubiquitous. To avoid danger, people
often exert self-control over their behavior (Baumeister, 1998;
Baumeister, Heatherton & Tice, 1994). When people fail to
exert self-control and behave more impulsively, they may
unintentionally put themselves in harm’s way (Freeman &
Muraven, 2010). Pedestrians jaywalk across busy streets,
children stick objects into electrical outlets, and teenagers
join dangerous gangs. The failure to exert self-control
and avoid these dangerous activities is likely affected by
many individual variables (e.g., demographics, personality).
However, a common mechanism that may be responsible for
human and nonhuman self-control vigor may also play a role
(Miller, Pattison, DeWall, Rayburn-Reeves & Zentall, 2010).
The present research tested this hypothesis by examining
whether dogs approach dangerous situations when their ability
to exert self-control is compromised.
Research with human and nonhuman animals suggests
that self-control relies on a limited resource (Baumeister &
Heatherton, 2004; Miller et al., 2010). Exerting self-control
depletes this resource, and once depleted, subsequent efforts
to control behavior become impaired. For example, when
humans control their impulse to eat fresh cookies (in comparison
to when they inhibit eating radishes), they then
persist for a shorter time on an unsolvable puzzle task
(Baumeister, Bratslavsky, Muraven & Tice, 1998). Dogs
behave similarly. When dogs control their physical movement
(in comparison with when self-control is not needed
because they are physically constrained by a cage), they
persist for a shorter duration on a subsequent unsolvable
puzzle task (Miller et al., 2010).
Extensive research with humans suggests that this phenomenon
is domain general, suggesting that tasks that require selfcontrol
negatively affect performance on a wide variety of
subsequent tasks (for a review, see Baumeister, Schmeichel &
Vohs, 2007). Decision making, for example, is negatively
affected by initial self-control exertion. Depleted subjects, as
compared with their nondepleted counterparts, take more risks
and gamble more (Bruyneel, DeWitte, Franses & Dekimpe,
2009; Freeman & Muraven, 2010; Molet, Miller, Laude, Kirk,
Manning & Zentall, 2012). To date, however, there is no
evidence that initial self-control exertion affects subsequent
H. C. Miller (*) : M. Molet
Université de Lille, Nord de France,
Domaine universitaire du “Pont de Bois”, Rue du Barreau,
BP 60149, 59653 Villeneuve d’Ascq Cedex, France
C. N. DeWall : K. Pattison : T. R. Zentall
University of Kentucky,
Lexington, KY, USA
Psychon Bull Rev
behavior in more than one domain for nonhuman animals, nor
is there evidence that depleted humans or nonhuman animals
are more likely to inadvertently subject themselves to risks that
may result in physical harm.
Some recent evidence suggests this possibility, because
self-regulatory depletion increases approach motivation
(Schmeichel, Harmon-Jones & Harmon-Jones, 2010) and
behaviors with an approach-related motivational direction,
such as aggression (Denson, Pedersen, Friese, Hahm &
Roberts, 2011; DeWall, Baumeister, Stillman & Gailliot,
2007; Finkel, DeWall, Slotter, Oaten & Foshee, 2009).
Consequently, the purpose of the present investigation was
to determine whether self-regulatory depletion has domaingeneral
consequences on nonhuman animal behavior and to
examine the likelihood that depletion would cause dogs to
put themselves in harm’s way by approaching a physically
threatening target. We chose dogs, in part, because, like
humans, they are highly social animals that establish social
dominance hierarchies and need to be sensitive to social
cues provided by other members of their species.
We adopted a two-task procedure used widely in the
human self-control literature (Baumeister, Bratslavsky,
Muraven & Tice, 1998). Dogs were tested twice, individually,
and we varied the requirements of the first task between
sessions. In the first task, either the dog was required to sit
still for 10 min (self-control depletion), or the movement of
the dog was constrained by placing it inside of a cage for the
same duration (control). Next, the dog was brought into a
room in which it encountered a caged, barking, and growling
dog. Dogs spent time in this room, but their behavior
was unconstrained. Thus, dogs could choose to spend their
time near the aggressor, or they could stay farther away.
Although dogs are predisposed to approach and investigate
unknown conspecifics (Lindsay, 2000), in this context, it
was the more dangerous thing to do. Greater proximity to a
confined aggressive dog, despite the confinement, is associated
with a greater risk of an aggressive encounter (American
Veterinary Medical Association, 2011; Lindsay, 2001, 2005;
Sacks, Sattin & Bonzo, 1989). Consequently, staying near the
aggressor was defined as the riskier (more impulsive) choice,
and avoidance was defined as the safer (less impulsive)
choice. We predicted that self-control depletion, as compared
with the control condition, would increase approach-related
behavior toward the threatening dog.
We recruited 10 dogs (Canis familiaris; 4 males, 6 females)
ranging from 12 to 120 months of age (M 0 48.8 months).
All dogs belonged to private owners, would immediately
approach a friendly caged dog, and had been trained to
maintain an out-of-sight sit–stay for 10 min. They had also
been trained to remain calm inside a cage for as long as 6 h.
A bath mat was placed on the floor in front of an empty dog
cage (1.2 m long × 0.8 m wide × 0.9 m high) that was
surrounded by a ProSelect™ exercise pen (see Fig. 1). The
dogs sat on this mat during the self-control manipulation.
This mat was placed inside a second dog cage (0.9 m long ×
0.6 m wide × 0.7 high) at the same location during the
control condition. A mirror was placed strategically on the
wall so that the experimenter could watch the dogs from
outside of the room through a small opening in the door. To
increase the difficulty of the self-control depletion phase, an
electronic “hamster” (Zhu Zhu pets®) was placed inside an
Adventure Ball™ and was activated inside the room during
the self-control depletion phase (see Fig. 1).
A highly dominant dog (an 11-year-old female bull terrier)
with a disposition for guarding territory was placed in a
dog cage (1.2 m long × 0.8 m wide × 0.9 m high) that was
surrounded by the ProSelect™ exercise pen. This dog
would bark and growl continuously whenever it was confined
and another dog was visible. The intensity of this
display was greater when its owner was close by, suggesting
that the dog included its owner as part of its territory to
defend (Borchelt, 1983; Lindsay, 2001). For this reason, the
owner (O) stood next to the dog during testing.
Fig. 1 The experimental room as it was set up for the self-control
manipulation that preceded the impulsivity test
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For safety reasons, the pen that was placed around the cage
provided an additional distance of 0.3 m between the aggressive
dog and the subject dog. The room (3.9 m long × 3.8 m
wide) was demarcated into zones by lines made with Scotch®
masking tape (2.5 cm wide; see Fig. 2). The first of four lines
was 61 cm from the screen (zone 1), and zone was 61 cm deep
(zones 2, 3, and 4). Because there were doors in zones 1 and 4
and standing near a door should be considered an escape
behavior rather than an approach behavior, we chose to define
this zone separately. The dog was considered in door space if
its front two feet were within 30 cm of the door and the dog's
body was pointing in the direction of the door.
In the first phase of the experiment, the door (B) was left
slightly ajar; however, both doors were closed during the
second phase of the experiment. Two video cameras were
used to record each testing session; one was mounted on a
tripod to the left of the aggressive dog, and an experimenter
who was to the right of the dog operated the other camera.
Pretesting At least 1 week before testing, all subject dogs
were introduced to a friendly caged dog. All subject dogs
approached the caged dog upon being released from leashed
restraint. The purpose of this testing was to ensure that
subject dogs were predisposed to approach an unknown
conspecific and that some level of inhibition would be
required for avoidance. In addition, subject dogs were
leashed and were exposed to the Zhu Zhu® hamster to
ensure that they were interested in but not frightened by it
when it moved. This assessment eliminated the possibility
that fear would confound the self-control manipulation.
Testing All dogs were tested with both conditions of the
self-control manipulation (order was counterbalanced). In
the self-control depletion condition, the dog was cued to
“sit” and “stay” by Experimenter 1 (E1). Following the cue,
E1 activated the Zhu Zhu® hamster and exited the room
through door A while the dog maintained its position. The
hamster was used to increase the difficulty of the selfcontrol
task. With the door slightly ajar, E1 watched the
dog (without being seen by the dog) via a strategically
placed mirror. The dog was allowed to keep visual track of
the hamster but if the dog moved from its position, E1
returned and gave the sit–stay cue again. A second experimenter
(E2), who stood outside of the testing room (behind
door A), recorded the number of cues and the time at which
each cue was given. The dog remained alone in the room
with the electronic hamster for a total of 10 min.
When the dog was released, it was given a small piece of
wiener (1 g), was moved to an adjacent room, and was
praised for 30 s by E1. After the subject dog left the testing
room, the aggressive dog was led into the newly vacant
room through door B by its owner (O) who was blind to
the self-control manipulation. The aggressive dog was
placed inside the cage, and O stood next to the cage behind
the exercise pen during testing. Once the aggressive dog was
situated, E1 entered the room with the subject dog (which
caused the aggressive dog to start barking and growling),
quietly walked the subject dog across the room on leash, and
unleashed it at a predesignated spot without further interaction
(black dot in Fig. 2). E1 then filmed the subject dog’s
behavior for 4 min while quietly standing still and looking at
the dog only via the screen of the digital camera. At the end
of 4 min, E1 leashed the subject dog and removed it from
the experimental room through door B.
In the control condition, E1 placed the subject dog inside
a dog cage and was told by E2 to return to the dog and
“recue” it to get inside of the cage at the same times she had
previously cued the dog during the self-control condition. If
the dogs’ first test session was in the control condition, it
was revisited by E1 three times at minutes 1, 5, and 7 during
the 10 min. This was the average number of revisits required
in a previous experiment (Miller et al., 2010). During the
control condition, the electronic hamster was inside the
room but was not activated. Pilot research indicated that
the hamster attracted attention from dogs during the sit–stay
but that, when activated while caged, it caused some dogs to
whine, circle, and paw. The remaining procedural variables
were held constant between conditions. Dogs were tested
between the hours of 09:00 and 15:00. A video clip displaying
the dogs’ behavior during the control manipulation
can be found at http://www.youtube.com/watch?
An observer, who was blind to the subjects’ condition,
Fig. 2 The experimental room as it was set up for the impulsivity test used a digital stopwatch to time the duration that subject
Psychon Bull Rev
dogs spent in each zone. A second blind observer coded
10% of the observations to obtain a reliability measure.
There was a positive Pearson correlation between the two
observers, r 0 .99, p < .01.
The dogs responded differently in the two conditions. The
dogs generally spent more time in zone 1 and near the doors,
especially following the self-control condition. The proportion
of time spent in each zone and near the door appears in Fig. 3.
A two-way repeated measures analysis of variance
(ANOVA) analyzed the differences of time spent in the
zones (+doors) across conditions (self-control, control).
Time spent in the room did not differ as a function of
condition because total time was equated, but the time spent
in the zones was significantly different, F(4, 36) 0 5.06, p <
.01, and the dispersion of time spent in zones was significantly
affected by self-control condition, F(4, 36) 0 2.56,
p 0 .05. Subsequent analyses were run to examine the
observed differences. A one-way repeated measures
ANOVA examining the effect of zone for the self-control
condition found that there was a very reliable effect of zone
following self-control exertion, F(4, 51) 0 6.08, p < .01, but
not following the control condition, F(4, 51) 0 1.88, p 0 .13.
When the simple effects of zone within each condition (selfcontrol,
control) were analyzed, it was observed that following
self-control exertion, dogs reliably spent more time in
zone 1 than in 2, 3, and 4, F(9, 36) 0 13.29, 15.75, 16.17,
respectively, all ps < .01, but not more time than near the
doors, F(9, 36) 0 3.67, p 0 .06. Following the control
condition, dogs did not spend a significantly different
amount of time between zones 1 and 2, F(9, 36) 0 2.13,
p 0 .15, but they did spend a significantly greater time in
zone 1 than in zones 3 and 4, F(9, 36) 0 5.67, 5.54, all
ps 0 .02. Here again, time spent in zone 1 did not differ from
time spent at the doors, F(9, 36) 0 1.95, p 0 .17.
Planned comparisons using two-tailed correlated samples
t-tests were performed on the difference scores in each zone
between the two conditions. The difference was significant
in zone 1, t(9) 0 3.11, p 0 .01 (dogs spent more time in zone
1 following the self-control condition), and in zone 2, t(9) 0
2.39, p 0 .04 (dogs spent more time in zone 2 following the
control condition), but it was not significant in either of the
other two zones (or near the doors), all ts < 1.2. As was
predicted, self-control depletion caused dogs to spend a
greater percentage of time in the zone nearest to the aggressive
dog (58.9%), as compared with the control condition
(41.8%). The data from individual dogs in both the selfcontrol
and control conditions appear in Fig. 4.
Avoiding danger enhances an animal’s ability to survive and
reproduce. Yet there are often occasions when the need to
avoid danger is paired with a natural tendency to approach.
To keep out of harm’s way, animals override their natural
impulse to approach in order to remain safe and secure.
When animals have limited self-control resources, they
may make more impulsive decisions that put them in harm’s
way. The present experiment examined whether initial exertion
of self-control would increase impulsivity in dogs,
resulting in risky decisions.
Our results supported this prediction. When dogs were
depleted, as compared with when they were not, they were
less able to inhibit their predisposed approach behaviors. As
a result, dogs approached an aggressive dog more when
depleted than when nondepleted.
Our interpretation of the present results rests on the
assumption that it is dangerous to approach a confined
aggressive dog and that subject dogs were risking their
safety by approaching. Although in the context of the present
experiment, strict precautions ensured the safety of all of
the dogs, confinement is not fail-proof in the natural world,
and it is quite possible that a confined aggressor could
escape and attack. Mail carriers are often attacked by presumably
confined dogs, as are children, and a significant
percentage of pet-related human fatalities result when a
restrained aggressive dog is approached (Sacks et al.,
1989; U.S. Postal Service, 2011). Moreover, moving away
from an aggressor defending its territory reduces the motivation
for attack (Lindsay, 2001).
present experiment, experimenters observed that the
aggressor displayed a more intense threat display when
subject dogs were near the fence and the intensity decreased
as subject dogs moved farther away. This observation
is similar to others regarding territorial behavior and
confinement (Calhoun, 1962; Klopfer, 1969; Lindsay,
2001; Pettijohn, Davis & Scott, 1980). It is also evidence
that approaching was relatively more risky than avoiding
the caged aggressor.
Another way of looking at the dogs’ behavior is as an
increase in counter aggression, provoked by the confined
aggressor. This complementary hypothesis is founded on
research demonstrating that humans, who typically suppress
emotionally driven aggressive responses, are more
likely to retaliate aggressively when they have depleted
their self-control. More specifically, when students initially
deplete their self-control by inhibiting their consumption
of a donut (but not a radish), they are less able
to control their aggressive behavior when they are subsequently
provoked (i.e., they are negatively evaluated
on a previously written essay). Depleted students retaliate
by adding more hot sauce to food intended for the
essay evaluator. Similarly, when students are initially
required to control their attention (inhibit reading words
displayed to them) and are subsequently given a negative
essay evaluation, they are more likely to administer
aversive noises to the essay evaluator. Furthermore,
following self-control exertion, students are more likely
to report the desire to inflict physical harm on someone
who provokes them (DeWall et al., 2007).
In the context of the present experiment, it is difficult to
delineate the role that increased aggression may have
played. Increased approach behavior may reflect counter
aggression, or it may reflect an increase in approach motivation.
Self-regulatory depletion increases approach motivation
in humans in the absence of aggressive intentions
and, thus, may have also contributed to the pattern of behavior
we observed in dogs (Schmeichel et al., 2010).
The commonality between human and nonhuman animals
is great, and the present research is further evidence
that human self-control has phylogenetic roots. It is also
further evidence that a phenomenon (i.e., depletion) once
believed to be uniquely human can be modeled with
dogs. Such modeling may have great empirical value,
since it may provide greater insight into the physiological
and neurobiological processes that affect self-control
vigor. Research with animal models will not supplant
that on cognitive factors involved in human selfregulation,
but it will augment our understanding of the
fundamental and biological rudiments of a phenomenon
that is clearly multifactorial in nature. Therefore, we
believe that social psychology will benefit by incorporating
work with nonhuman animals to extend existing
Author Note We thank Byron Nelson for his help with data analysis.
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